The general composition and method of preparing phenolic foam are well known. Generally, a foamable phenolic resole composition is prepared by admixing aqueous phenolic resole, blowing agent, surfactant, optional additives and an acid curing agent into a substantially uniform composition. The curing catalyst is added in amounts sufficient to initiate the curing reaction which is highly exothermic. The exotherm of the curing reaction vaporizes and expands the blowing agent thereby foaming the composition. The foaming process is preferably performed either in free-rise or closed mold type operations.
The general method for the continuous manufacture of phenolic foam insulation board generally involves preparing a foamable phenolic resole composition by continuously feeding into a suitable mixing device the aqueous phenolic resole, blowing agent, surfactant, optional additives, and acid curing catalyst. The ratio of these ingredients is adjusted depending on the density, thickness, etc. desired in the final product. The mixing device combines these ingredients into a substantially uniform composition which is continuously applied evenly onto a moving substrate, usually a protective covering such as cardboard, which adheres to the foam. The foaming composition is usually covered with another protective covering such as cardboard which becomes adhered to the phenolic foam. The covered foaming composition is then passed into a double belt press type apparatus where the curing exotherm continues to vaporize and expand the blowing agent, thereby foaming the composition as it is cured.
In the preparation of foams of this kind, one of the important objectives is to obtain foams that have a relatively low density and are homogeneous in cross section. The result often depends on the extent of dissolution in the foamable resin, and the ready conversion, of the dissolved blowing agent which provides the gaseous blowing medium. When fluorocarbons are used as blowing agents, a problem may arise because of insufficient solubility of the blowing agent in the resin or from the compatibility of the fluorocarbon blowing agent, trichlorotrifluoroethane, CFC-113, in the system. Suitable fluorocarbon solubility in the system is important for at least the following reasons:
(a) to insure metering of stoichiometric correct amounts of two component systems on commercial foam production equipment; and
(b) to increase the amount of fluorocarbon blowing agent in the closed-cell structure of resultant rigid phenolic foams to produce optimum insulation properties.
While a variety of chlorofluoroalkane blowing agents have been used for phenolic systems in the past, none of the known systems which have been employed heretofore have been entirely satisfactory. In phenolic foam systems, if the fluorocarbon blowing agent is not completely soluble or miscible in the "premix" component of the system (i.e. resole resin, surfactant, fluorocarbon blowing agent or other additives), the insoluble portion of the fluorocarbon will separate as a distinct layer on the bottom of the "premix" component container during storage. When the "premix" component container, e.g. 55 gallon drum, is put into use for phenolic foam production, processing, foam appearance and physical property problems could arise because the "premix" component is not homogeneous. The resulting consequences of a non-homogeneous pre-mix are such as lack of uniformity of product, poor appearance and physical properties such as excessive density.
Fluorocarbons, as a class of insulating gases that are contained in the foam, exhibit the lowest thermal conductivity values when compared to other gases such as air, nitrogen, carbon dioxide, water vapor, etc. In many foam systems, fluorocarbons not only act as blowing agents to produce the foam by virtue of their volatility, but also are encapsulated or entrained in the closed cell structure of the rigid foam and are the major contributor to the low thermal conductivity properties of foams used in insulation applications.
If the required amount of fluorocarbon is not present in the resultant rigid foam due to insolubility of some of the fluorocarbon in the foam system then the processing characteristics of the foam system will change and desired foam appearance and physical properties, e. g. density, loadbearing, thermal conductivity, etc. would not be achieved. Therefore, it is necessary for the fluorocarbon to be homogeneously dispersed in the foamable resin system in order to obtain the desired results.
Accordingly, a need exists for an improved blowing agent for rigid phenolic foam systems which have the desired solubility, compatibility and stability and which does not adversely affect the resultant rigid foam properties.